<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
     /*   body{
            margin:0;
        }*/
        /*把所有标签自带的间距都去除*/
        *{
            margin:0;
            padding:0;
        }

        div{
            width:150px;
            height:150px;
            background-color: #ff6700;
        }
        .box2{
            background-color: darkred;
        }
        .box3{
            background-color: darkcyan;
        }

    </style>
</head>
<body>
<h2>我是一个标题</h2>
<p>我是一个段落</p>
<ul>
    <li>列表项</li>
    <li>列表项</li>
    <li>列表项</li>
    <li>列表项</li>

</ul>
<div class="box1"></div>
<div class="box2"></div>
<div class="box3"></div>

</body>
</html>